The purpose of this project is to identify quantitatively the posture control characteristics of the normal and vestibular-deficient human in an upright attitude. The vestibulospinal and converging visual and proprioceptive mechanisms will be studied by identifying the transfer characteristics between motions detected by the vestibular system in the subject's head and his center-of-mass trajectories. Performance of normal subjects under stable and unstable conditions should provide additional information about the characteristics of the vestibulo-spinal and its converging control systems which will in turn provide a rapid screening method for evaluation of patients complaining of spatial disorientation.